Hollow blade for turbines



Dec. 12, 1933. LORENZEN HOLLOW BLADE FOR TURBINES Filed Jan. 17, 1930 Patented Dec. 12,\'1933 v 1,939,357 noLLow BLADE Fon 'rUnBrNEs Christian Lorenzen, Berlin-Treptow, Germany, assigner,` by mesne assignments, to Bendix Aviation Corporation, Chicago, lll., a corporation oi' Delaware Application January 17, 1930, Serial No. 421,424, I

13 Claims.

` In certain constructions of steam or gas turbines there yare employed frequently hollow blades, which are made either by pressing tubular sheet metal blanks into the well-known crescent shape, or by joining two blade sections or halves. Since sheet metal can not be bent very sharply, these old methods do not permit the edges of the blades, at the tips of .the crescent, to be given such a sharpness'or slenderness as is desirable in order to enable lthe driving jet of steam or gas to perform its action efficiently and without jerks.

For the purpose 'of overcoming the diillculty pointed outl above, I have devised the presentimprovement, according to which the body of the hollow blade may still be madeof sheet metal, but the edges at which the driving medium enters and leaves respectively, are made on separate elements or strips which are connected with the Atubular body by soldering, welding, etc., whereupon the edges of such strips can be milled, filed or otherwise worked to the desired sharpness, shape, and smoothness of surface. This improvement also enables me to usevery thin, soft material for the ybody of the blade, and thus to reduce the cost',

while the .edge strips, where the wear is greatest, are made of a material harder and more resistant than that of said body. This construction also presents the advantage that after the edge strips have become worn, the blade may be restored to eiilciency, by removing the edge strips and substituting new ones, thus avoiding a complete 4renewal of the entire blade.

It will be evident that since the edge strips are made of solid material and therefore relatively heavy, they will cause an increase of the strains produced by centrifugal force in the tubular blade body during the operation of the turbine. To take proper care of these increased strains, I prefer to reinforce the tubular body at the inner-end or foot, either by an increase in the thickness ofthe body material l:toward the foot, which 4increase may extend over the entire length of the body or only part of it, or by the addition of separate reinforcing material'at the foot, which reinforcement would be connected with thebody of the blade (either on the inside or on the outside) in any suitable manner, as by welding, soldering, or

like operations.

The edge strips consisting of solid material may; `ual as shown and the corresponding end of the also be made integral with the foot, in which case the thin sheet metal walls forming the' crescent shaped portion of the blade would preferably be secured to the outer faces' of such edge strips.

Several typical and satisfactory embodiments of my present linvention are illustrated by the accompanying drawing, in which Figs. 1 and 2 are cross sections showing two forms of my improved turbine blade, and Figs. 3, 4,'5'and 6 are partial longitudinal sections, Figs. 3, 4 and-5, and the left hand portion of Fig. 6. being taken in the plane and in Germany February 13, 1929 indicated at 3;-3 in Fig. 1, and illustrating four different ways of connecting the edge strips with the body and the foot of the blade.

According to Fig. 1', the blade body a is made of sheet metal and forms a complete tube. The

and more durable (resistant) metal than the body a, are secured t the outer faces of the said body, at the bends thereof, in any suitable manner, as by welding or soldering. These edge strips are very sharp at their free ends, much sharper than couldbe formed on the body a by bending, and thus are considerably more eificient as regards guiding the driving medium (steam or gas) and insuring its jerkless action. The edge strip may be machined or otherwise fashioned to its nal shape, before attaching it to the blade body a; or, as indicated by dotted lines at the right of Fig. 1, the edge strip may be originally of greater thicknessand milled, filed, or otherwise worked edge strips b, which are preferably of a harder down to the final shape (shown in full lines) after 'the strip has been attached to the blade body. In either event, the edge strip is made with a proper groove or concavity to form a seat for the bend of the blade body a.

According to Fig. 2, the blade body, instead of being formed of atubular member a, consists of two separate -pieces a' of sheet metal, ofproper curvature to form the hollow crescent ofthe blade. The edge strips b' are here shown as formed with shouldered recesses into which are fitted the edges of the two body members a', each edge strip b' thus having an inner portion projecting between the said body members and sup.

porting or backing them eiciently. Theconnection of the edge strips b' with the body members a' may be effected by soldering or welding, as described with reference to Fig. 1.

In both constructions shown in Figs. l and 2, the convex and the concave outer surfaces of the blade body are flush with the adjacent surfaces ofthe edge strips.

, A s regards the formation of the blade at its inner end or foot, the following constructions are illustrated .in Figs. 3 to 6:

In Fig. 3, the body member a is thickened at the foot portion,'and formed integral therewith, the increasein thickness being preferably lgradedge strip b being tapered to nt. At d I have inucated, in Figs. 3 to 6, a groove adapted to receive a corresponding flangev or projection on the which is applied, as a ring, on the outer surface:

of the body member' a and is connected therewith,

to the interior of the blade body a, instead of externally as in Fig. 4. In Fig. 5, the blade body a is therefore interposed between the reinforcing member and the edge strip, and the latter is not in contact with the reinforcing member c'.

Fig. 6 illustrates a construction in which the annular reinforcement c (similar to the ring c of Fig. 4)k is made integral with the edge strip b, the blade body a being shown as of uniform thickness in Figs. 4, 5, and 6.

It will be. noted that the 'internal reinforcement c shown in Fig. 5 may also function as a closure for the interior of the hollow blade, at the inner end or foot thereof; such closing of the inner blade end may be desirable or necessary in some cases.

While Figs. 3 to 6 show constructions in connection with an arrangement such as illustrated by Fig. 1, where a bend of the body a fits into-a groove of the edge strip b, it will be understood that formations substantially like those shown in Figs..3 to 6 may also be used in conjunction with a blade construction such as illustrated by Fig. 2. I prefer, however, to use constructions in which the main portion a of the body consists of seamless sheet metal tubing as shown in Fig. 1, with the ends of the crescent-shape curved to form convex outer surfaces forming seats for `the concave inner surfaces of the edge strips b.

Various modifications may be made without departing from the nature of my invention as defined in the appended claims.

I claim: V

1. A hollow turbine blade having a body of thin metal, and an external solid reinforcing strip connected with said body forming an external longitudinal operative surface therefor and said strip having means thereon for securing the blade to the turbine.

2. A hollow turbine blade having a sheet metal body of general crescent shape, externalI solid reinforcing strips connected with said body and forming two external longitudinaledge strips therefor at the ends of the crescent shape, said strips forming operative surfaces for the blade and a reinforcing member, integral with said edge strips, secured to the blade body and located at the inner end or foot thereof, and means on Isaaid member for attaching the blade to the tur- 3. A hollow turbine blade having a` body of thin metal, an external solid reinforcing strip `connected with said body and forming 'an external longitudinal edge strip therefor, said strips forming operative surfaces of thev blade and a reinforcing member integral with said yedge strip and located at the inner end or foot of the blade, and a flange on said member for tively hard reinforcing strip connected with said body and forming an external longitudinal operative edge therefor, said strip having means for securing the blade to the rotor of the turbine.

6. A hollow turbine blade having a body of relatively soft thin metal, and an external relatively hard reinforcing strip connected with said body and forming an external longitudinal operative edge therefor, said strip having an external groove for securing the blade to the rotor of the turbine.

7. A hollow turbine blade having a sheet metal bod'y of general crescent shape, and external solid reinforcing strips connected with'said body and forming two external longitudinal operative edges therefor at the ends of the crescent-shape, said strips having means for securing the blade to the rotor of the turbine.

8. A hollow turbine blade having a sheet metal body of general crescent shape, and external solid reinforcing strips connected with said'body and forming two external longitudinal operative edges therefor at the ends of the crescent-shape,

said strips having external grooves for securing the blade to the rotor of the turbine.

9. A hollow turbine blade having a sheet metal body of general crescent shape, and an external solid reinforcing strip connected with said body and forming an external longitudinal operative edge therefor at an end of the crescent shape, the outer surfaces of said strip being flush with the adjacent outer surface portions of the body, said strip having'means for securing the blade to the rotor of the turbine.

10. A hollow turbine blade having a relatively soft sheet metal body of general crescent shape,

and an external relatively hard reinforcing strip l connected with saidv body and forming an ex-I ternal longitudinal operative edge therefor at an end of the crescent shape,`the outer surfaces of said strip being flush with the adjacent outer surface portions of the body, said strip having an external groove for securing the blade to the rotor of the turbine.

11. A hollow turbine blade having a` body of thin metal, an external solid reinforcing strip lconnected'with said body and forming an external longitudinal edge strip therefor constituting a Working surface of the blade, and an ann nular reinforcingl member located at the inner end or foot of the blade and having means for securing the blade to the rotor of the turbine.

l2. A hollow turbine'blade having a body of thinI metal, an external solid reinforcing strip connected withvsaid body and forming an external longitudinal edge strip therefor constituting a working surface of the blade, and an annular reinforcing member located at the inner end or foot of the blade and having an external groove for securing the blade to the rotor of the l turbine.

13. A hollow turbine blade having a body of metallic tubing of general crescent-shape with bends at the ends of the crescent-shape, the

outer surfaces of said bends being convex, and

external solid reinforcing edge strips having concave surfaces fitted against the said convex surfaces of the body and secured thereto and forming two external longitudinal working edges for y said'body at the ends of the crescent-shape.

- CHRISTIAN LoRENzENJ 

